34330A 30 A Current Shunt any cheaper alternative?

"Myauk" schreef in bericht news: snipped-for-privacy@35g2000pry.googlegroups.com...

Farnell offers a couple of 60A shunts for about 40 euro - roughly 80 Singapore dillars. They also offer a wide variety of "low Ohmic value" and "power metal strip" resistors, with values down to 1milliohm and tolerances as a good as +/-1% at prices that run aound one euro/two Singapore dollars - but the minimum order qunatity is a least five.

--
Bill Sloman, Nijmegen

Some of us don't call them shunts, we call them power resistors. Heck, often they're just pieces of resistance wire. Back in the good old days, when men were REAL men, women were REAL women, and small fuzzy creatures from Alpha Centauri were REAL small fuzzy creatures from Alpha Centauri, we all took basic meter movements and use resistors to get the voltage or current measurement range we actually needed.

If you put 4A through a 0.05 ohm resistor, you have a 0.2V drop across the resistor. So with a DMM set to 200mV full scale you see 1A as

50mV, 2A as 100mV, 3A as 150mV, 4A as 200mV, etc.

If you need less voltage drop across the shunt, you use a lower-ohm resistor. Also look at power dissipation. Putting 4A through a 1/4 watt 0.1 ohm resistor won't work for very long!

Some manufacturers call these small ohmic values "current sense" resistors. Some, especially the milliohm values, are available as "4- wire" configurations to remove the error caused by the resistor lead voltage drops.

I don't know about Singapore, but here in the US these are standard stock items at Mouser and Digikey etc.

Tim.

On a sunny day (Thu, 8 Jan 2009 15:11:24 +0100) it happened "Bill Sloman" wrote in :

Conrad.nl has 50A shunts for 14Euro95

$ROOT&p_artikelbilder_mode=&p_sortopt=&page=&p_catalog_max_results=20 .5 percent, they have lots of shunts. conrad is prety good these days, no postage above 25 Euro, just got some stuff from them.

I'll echo what everyone else says.

- search for "resistor", then look at the category for either current sense or wirewound resistors. Then look for the appropriate power rating. Between 2W and 10W, both categories list a bunch of parts for between $2 and $20.

Chris

Here's one for about $30 USD

Murata should be easily available in Singapore.

I've used a few off Ebay item number 350138498285 (China) . Very nice

50A shunts at $20 USD. They also throw in a panel DVM for free. (not GPIB though).

I know, but, what I don't know is why Agilent is asking so much money around 300 S$ for calibration!

What is it so special in agilent 34330A ?

Is it because it is an Agilent product?

:)

Regards

? o

The reason might be tolerance at that resistance value, it think.

Because if you really need the paperwork (certificate) you'll pay for it. It costs money to run a NIST-tracable metrology lab, and many people don't need the certificate.

With inexpensive stuff it may be cheaper to throw it away at the end of the calibration interval. Certainly that is the case with mechanical gage blocks.

You've probably already spent more $ worth of time than it's worth at the overheaded cost of a good test engineer, assuming you only need one.

Anyway, the list price from Agilent (also Allied, Newark etc.) for the

34330A 30A 0.3% shunt is only $81 USD, which is less than $120 SGD. Pretty reasonable, considering it has a housing and four bananna plugs/jacks, and is from a generally reputable manufacturer.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
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Also they are very common swap meet items.

I'm not sure I'd be using a wirewound device. The shunts I have look like a piece of copper mounted on an insulator and set up for 4 terminal (Kelvin) measurement.

They should be a low tempco alloy (eg. Manganin) and they should be made to be fairly non-inductive. Copper has a high tempco (like most elemental metals) of around +3900ppm/K at room temperature.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Two large copper blocks, with screw terminals, are the dominant features of shunts. The resistance element is manganin, which has zero resistance tempco.

The large copper blocks, and the user's heavy copper current-carrying wire are important for heat removal from the manganin element. A common power resistor, even if equipped with Kelvin terminals, cannot match the performance of a shunt.

I use Empro shunts,

Yes, I have used a whack of 15kA shunts (and some smaller ones) like those in a plating installation.

The large copper blocks/heatsink fins/water cooling is/are probably a bit excessive for the OP's application, which would likely only involve dissipating 0.160W maximum. ((4A)^2 * 0.01 ohms).

Here's another supplier-- this one goes down to 5A/50mV.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

The Wikipedia article claims that Manganin has "virtually zero temperature coefficient of resistance value" - true, but only within a small temperature range. Only your last reference provides a resistance vs temperature curve for their specific alloy of manganin; some other manganin alloys are significantly worse and they all have exactly zero tempco only at one specific temperature.

Some interesting details on resistance alloys can be found in the ASM Metals Handbook vol 2, Nonferrous Appoys and Special Purpose Materials, in the Electrical Resistance Alloys section, including curves for a number of alloys showing the variation of a 75Ni-20Cr-3Al alloy to be about an order of magnitude less than the best manganin.

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"The Journey is the reward"

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You have a point. Probably an alloy since it didn't have a weathered look of copper.